WO patent specification 95/27600, example 2, discloses a wood preservative comprising, in addition to zinc and copper acetate, ammonium acetate and preferably a quaternary ammonium compound, such as didecyl dimethyl ammonium chloride.
U.S. Pat. No. 4,929,454 (column 2, line 60-column 3, line 6) discloses a method for preparing wood by impregnating wood with zinc, copper and a quaternary ammonium compound, which may consist of tertiary C8-C20 alkyl ammonium salt of fatty acid. However, the use of copper and zinc may cause environmental and corrosive problems.
EP patent specification 1 114 704 A2 discloses a wood preservative without copper and zinc, which contains water-soluble organic ammonium carboxylate. The ammonium ion of this quaternary ammonium carboxylate comprises a C1-C20 alkyl group or an aryl substituted alkyl group and at least one, preferably two alkyl groups containing 8-20 carbon atoms, cf. paragraph [0051] of the specification. The carboxylate may be e.g. acetate, cf. paragraph [0224], or propionate, cf. paragraph [0219]. In addition to a microbicide property, the preservatives containing quaternary ammonium carboxylates of the reference have enhanced retention, and they can even be used without metal stabilisers, such as combinations of arsene, chromium, copper and zinc, cf. paragraph [0032] of the reference.
However, the ammonium carboxylates of these references involve the problem of not being absorbed into wood in adequate amounts, or of having poor retention in wood.
There are several widely known agents which can be used for controlling insects such as termites:
Disodium Octaborate Tetrahydrate (DOT) is used against fungi, insects and termites. DOT maximizes the solubility, the rate of dissolution and the boric oxide content to give a borate active ingredient far superior to traditional boric acid or borax. At the levels used in professional applications, it prevents pest infestation by inhibiting pest metabolism on a cellular basis. The tetrahydroxyborate anion forms a chelate complex with the cis-adjacent hydroxyl groups in the ribose sugar of nicotinamide adenine dinucleotide (NAD), with the cationic nitrogen of the nicotinamide moiety providing electrostatic stabilization of the chelate. In this configuration, NAD and NADP cannot be used by the dehydrogenase enzymes of glycolysis, the pentose phosphate pathway or the tricarboxylic acid pathway, and so the cellular energy generating mechanisms, including adenosine triphosphate production, are shut down.
Permethrin is one of many synthetic pyrethroids. Permethrin is a neurotoxin and it is used against a variety of pests, on nut, fruit, vegetable, cotton, ornamental, mushroom, potato, and cereal crops. It is used in greenhouses, home gardens, and for termite control. It also controls animal ectoparasites, biting flies, and cockroaches. Permethrin kills insects by strongly exciting their nervous systems. Rather than sending a single impulse in response to a stimulus, permethrin-exposed nerves send a train of impulses, similar to that of the organochlorine insecticide DDT. Membrane ATPases are a target of the neurotoxic effect of pyrethroid compounds which could explain the effect on the immune apparatus. Permethrin is toxic to honey bees and other beneficial insects, fish, aquatic insects, crayfish, and shrimp. For many species, concentrations of less than one part per billion are lethal. Permethrin causes deformities and other developmental problems in tadpoles, and reduces the number of oxygen-carrying cells in the blood of birds.
The above mentioned agents used widely for insect control are relatively harmful for beneficial insects which will limit severely their use for example in wood treating; if these agents are impregnated into wood their concentration should be kept considerably low.
There are also several prior art methods for preparing wood, in which wood is impregnated with copper compounds, a reaction mixture or a complex of ammonium carboxylate and copper compounds (e.g. U.S. Pat. No. 6,352,583 and EP 238 051). Such wood preservatives have the drawback of using toxic copper compounds and/or of having poor retention in wood and/or poor absorption into wood.